I'm using a delegate for MyOpenId, and over about the past day, I've encountered the "Unable to log in with your OpenID provider: No OpenID endpoint found." error when trying to log in. I can log in with Google, but I still hit this problem even if I haven't already logged in to Google and I don't think of that as a permanent solution anyway.

I just finished a torrid time of determining how to make my delegate OpenID work with StackExchange sites, so I don't know what could be the cause this time. Immediately afterward, I tried logging into slashdot and SourceForge, both of which support OpenID authentication, and both signed me in without a problem.

Yeah, it works for me now, too. It was just a weird, 1-day error I guess. But, slowness didn't seem to be an issue for me, at least, because I visited my page and it loaded without any speed issue.
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palswimSep 13 '10 at 15:37

I've probably solved at least part of the issues. It turns out that my site has been having DNS issues, about which I didn't know. I don't know if it has fixed all of the OpenID issues I've had, but it certainly fixed the current one(s).

I found out that accidentally leaving out the <html> opening tag also yields the "No OpenID endpoint found" message when you use OpenID delegation. This is true for the DotNetOpenAuth library that Stack Overflow uses.

On the other hand, if the HTML is valid, the delegated OpenID login works even if only these two lines are to be found in the HTML header (for Google account in this case):